Method and device for controlling the curing rate of concrete

ABSTRACT

A method and device for controlling the curing rate of concrete comprising the measuring of the temperature of the concrete, assessing the momentaneous maturity of the concrete by means of the temperature variation and controlling the heat supply or dissipation on the basis of the momentaneous maturity in a manner such that at the end of the period the concrete has the desired maturity. A preferred embodiment of the device according to the invention comprises a temperature measuring device (15) to be connected to at least one temperature sensor (6,7), and a calculating device (16) connected to the temperature measuring device (15), assessing the momentaneous maturity and provided with a data input member (17) and a display member showing the assessed momentaneous maturity.

The invention relates to a method of controlling the curing rate ofconcrete comprising the step of influencing the heat supply ordissipation for a given period of time.

In the concrete building industry, for example, it is common practice toset up the casing for part of a building during the day, to pour theconcrete and to mount the heating device. During the 16 hours betweenthe end of the workday and the start of the next the fresh concrete isheated so that at the beginning of the next workday it is sufficientlystrong to permit of removing the casing. This casing can be set up againthe same day for pouring the concrete of a further part of the building.By heating the concrete the curing time of many days in a naturalprocess can be reduced to 16 hours between two workdays. In order toassess whether the concrete is, indeed, sufficiently strong to allowremoval of the casing, test cubes are made simultaneously with thebuilding part and also subjected to the thermal treatment. At thebeginning of the workday the strength of said test cubes is checked andif it is found sufficient, the casing can be removed. If it is foundthat the strength of the test cubes is not sufficient, the casing cannotbe removed so that it is no longer possible to set up this casing againthe same day for a next building part. In this case a whole workday islost.

It is assumed, of course, that the strength of the test cubes is, withreasonable accuracy, representative, of that of the concrete in thecasing. However, it has been found in practice that said accuracy ispoor. It may, therefore, occur that the casing is removed whereas thiswould not be allowed for reasons of strength of the concrete andotherwise that costly workdays get lost by not removing the casing whereremoval were allowed without hazards.

The object of the invention is to provide a method of the kind set forthin the preamble, which does not exhibit these disadvantages. For thispurpose the method embodying the invention comprises the steps ofmeasuring the temperature of the concrete, assessing the momentaneousmaturity of the concrete by means of the temperature course andcontrolling the heat supply or dissipation on the basis of themomentaneous maturity in a manner such that at the end of the period theconcrete has the desired maturity. The maturity of concrete ischaracterized as the integral of an exponential function of the concretetemperature with time. In this function a constant depending on the kindof concrete plays an important part. There has been shown a relationshipbetween the relative strength of the concrete and the maturity, whereinthe relative strength is the ratio between the strength at a giveninstant and the strength attained under standard conditions i.e. after28 days at 20° C. In a given kind of concrete a given relative strengthis associated with a given maturity. By regulating the maturity inaccordance with the invention by means of temperature-control, it can beensured that after a given period the concrete has attained a givenmaturity and hence a given relative strength.

Although in the foregoing reference is made to acceleration of curing ofconcrete by raising the temperature, the invention may also be appliedfor decelerating the curing process by temperature reduction.

In the method according to the invention the concrete temperature ispreferably measured at a plurality of areas, whilst the heat supply ordissipation is controlled on the basis of a given, momentaneous extremematurity at the measured temperature. With accelerated curing thisextreme maturity will be the lowest given maturity and with deceleratedcuring this extreme maturity will be the highest assessed maturity. Inthis way it is ensured that after a given period each part of theconcrete has obtained the desired properties.

A simple, but reliable operation is obtained when in accordance with theinvention the control is an on/off control on the basis of thetemperature variation of the introduced heat after cutting off the heatsupply or dissipation. The increase in maturity after cut-off of theheat supply or dissipation is estimated. When the real temperaturevariation differs from the expected temperature variation interventionis possible by switching on the heat supply or dissipation.

The invention also relates to and provides a device for carrying out themethod embodying the invention. This device comprises at least onetemperature sensor, for example, a thermocouple to be housed in theconcrete, a temperature measuring device to be connected to thetemperature sensor and a control-device connected to a data input memberto the temperature measuring device and to a heat supply or dissipationdevice. The data of the concrete, more particularly the relationshipbetween the maturity and the relative strength are introduced into thecontrol-device by the data input member.

The invention furthermore relates to and provides a device fordisplaying the momentaneous maturity of the concrete comprising atemperature measuring device to be connected to at least one temperaturesensor, and a calculating member connected to the temperature measuringdevice, assessing the momentaneous maturity and provided with a datainput member and a display member showing the assessed momentaneousmaturity. The method embodying the invention can thus be carried intoeffect by manually adjusting a heating device or the like in accordancewith the maturity displayed at a given instant. This device also permitsof checking the curing process in the case of a natural cure.

The device preferably comprises furthermore a display member for themomentaneous strength.

In the following description the invention will be explained more fullywith reference to the Figures.

FIG. 1 is a schematic, perspective view of a device under conditions ofuse, some parts being broken away.

FIG. 2 is a sectional view taken in the direction of the arrow II--II inFIG. 1.

FIG. 3 is a sectional view taken in the direction of the arrow III--IIIin FIG. 1.

FIG. 4 is a block diagram of the device of FIG. 1.

In a building 1 rising walls and a floor lying thereon are formed by acast construction method. The rising walls and the floor are made ofconcrete 5 poured between side casings 2 and a tunnel casing 3. Settingup the casings, the arrangement of the reinforcements (not shown) andpouring the concrete are performed in a single workday. Inside thetunnel casing 3 a heating device 10 is arranged for heating the pouredconcrete 5 for the period from the end of the workday to the beginningof the next workday so that the curing of the concrete is accelerated.Through the side casings 2 are passed temperature sensors 6, whichassess the temperature of the cast concrete 5 by means of a measuringpin 12. The top surface of the cast concrete 5 is also provided withtemperature sensors 7, for example, lying on the concrete 5. Thetemperature sensors 7 assess the temperature of the concrete also withthe aid of a measuring pin 12. The temperature sensors 6, 7 areconnected through leads 8 to the temperature measuring device 15 of thecontrol-device 9. The temperature measuring device 15 passes a number oftemperature values to a control-device 16. To the control-device 16 arefurthermore connected a data input member 17 and an adjusting member 18for the maximum temperature. The adjusting member may be connected to atemperature sensor which assesses the temperature in the spaceaccommodating the heater 10. Thus this space temperature and hence thetemperature of the surface of the concrete being in contact with thecasing can be prevented from becoming too high. The control-device 16may comprise a microprocessor which is programmed in a manner such thatit controls the heat regulator 19 by means of the data from thetemperature measuring device 15, the data input member 17 and theadjusting member 18 for the maximum temperature. By means of the datainput member the relationship between the maturity and the relativestrength of the concrete used can then be introduced. A furtherpossibility is that only data about the composition of the concrete needbe introduced, in which case the control-device 16 calculates theassociated relationship between maturity and relative strength andthereby controls the heat regulator 19. The heat regulator 19 controlsthe burner pump 20 through a lead 22, whilst a monitor 23 is coupledthrough a lead 21 with the heat regulator 19.

The control-device 16 may be programmed so that it switches on theheater after a given initial period in which the concrete solidifies.After the concrete has reached the set temperature, the heat supply iscontrolled so that this temperature is maintained. Subsequently, when agiven maturity is obtained, the heater is switched off. This assessedmaturity corresponds with the desired maturity at the end of the overallperiod minus the increase in maturity that can be expected after thecut-off of the heat supply up to the end of the period. This increase iscalculated by the control-device with the aid of data introduced andrelating to the expected temperature drop after the heat supply isswitched off. During the cooling period the control-device continuescomaring the real temeperature variation with the expected temperaturevariation. If it appears that the temperature decreases excessively, forexample, due to a change of weather conditions, the control-device 16will again switch on the heater, after which the control-processdescribed above is repeated.

As stated above, the method and device embodying the invention may beemployed, not only in the accelerated curing process described above,but also in a decelerated curing process. Decelerated hardening may bedesired for obtaining given properties of the material. Deceleratedhardening is obtained by keeping the concrete temperature low with theaid of heat dissipation.

The method and device embodying the invention provide an optimum heatingprocess or heat dissipation and thus reduce energy consumption ascompared with the methods hitherto known.

The method is described in the foregoing with reference to itsapplication in a cast concrete building process. Apart from thisapplication many other uses are conceivable, for example, in industrialmanufacture of concrete elements, prefabricated building parts and thelike. Where it is desired to influence a curing process this method canbe applied.

I claim:
 1. A method of curing concrete to a desired value of cureaccumulated over a specified period of time subsequent to pouringthereof, which desired value of cure would not be accumulated over saidspecified period of time under normal conditions, which comprises thesteps of:(a) controlling the temperature of the concrete over an initialperiod of time while the concrete progressively cures to an assesseddegree of partial cure thereof which, when augmented by that additionalcuring calculated to occur by the end of said specified period of timeon the basis of an expected temperature variation of the concrete in theabsence of such control, will yield said desired value of cure; and (b)monitoring further progressive curing of the concrete after said initialperiod of time and in the absence of said control by measuringtemperature variation of the concrete and comparing it with saidexpected temperature variation to detect disparity between said furtherprogressive curing and said additional curing as calculated, and furthercontrolling the temperature of said concrete when such disparity isdetected as would otherwise cause the concrete to accumulate a furtherprogressive curing significantly different from said additional curingas calculated.
 2. The method as defined in claim 1 wherein step (a)comprises controlling the temperature of the concrete by first bringingit to a set temperature and then maintaining said set temperature. 3.The method as defined in claim 1 including the step of monitoring thetemperature of the concrete during step (a).
 4. The method as defined inclaim 3 wherein the degree of partial cure of step (a) is assessed onthe basis of the temperature of the concrete during step (a).
 5. Themethod as defined in claim 2 including the step of monitoring thetemperature of the concrete during step (a).
 6. The method as defined inclaim 5 wherein the degree of partial cure of step (a) is assessed onthe basis of the temperature of the concrete during step (a).
 7. Asystem for imparting a desired maturity to concrete by the end of apredetermined time, which comprises:(a) temperature control means forcontrolling the temperature of the concrete; (b) sensing means forsensing the temperature of the concrete; and (c) calculating means forcalculating the moment at which the concrete has reached a partial valueof cure due to the temperature at which the concrete has been kept bysaid temperature control means which for an expected temperaturevariation over the remainder of time from said moment to the end of saidpredetermined time is calculated to provide an additive curing to yieldsaid desired maturity with said temperature control means inactivated,for inactivating said temperature control means at said moment, formonitoring the temperature variation of the concrete during saidremainder of time and comparing such temperature variation with saidexpected temperature variation to determine departure therefrom, and forreactivating said temperature control means in response to departurefrom said expected temperature variation that would otherwise cause theconcrete to accumulate an additive curing significantly different fromsaid additive curing as calculated.
 8. A system as defined in claim 7wherein said temperature control means comprises a heat supply, saidsensing means comprises at least one temperature sensor to be housed inthe concrete and a temperature measuring device to be connected to saidtemperature sensor, and said calculating means comprises a controldevice connected to a data input member, said control device beingfurther connected to said temperature measuring device and said heatsupply or dissipation device.